The contract will use the mouse model to address 1) the susceptibility to persistent infection following intradermal low-dose inoculation; 2) sequential immune response to tissue adapted spirochete antigens; 3) kinetics of spirochate growth in target tissues using quantitative PCR and 4) mRNA expression of spirochetes. The experiments will characterize the model for chronic infection and answer questions about mechanisms of persistence in the unaltered, immunologically responsive host.